How Interplanetary Internet Will Work

Six microsatellites like this one might be put into low Mars orbit to increase data return from Mars missions.

Photo courtesy NASA / JPL

Take a look at the the 1997 Mars Pathfinder rover mission and you will understand space explorers need an interplanetary Internet for deep space communications. Data from the Pathfinder trickled back at an average rate of about 300 bits per second during its mission. Most likely, your computer can transfer data at least 200 times faster than that. An Internet between Mars and Earth would likely yield a data transfer rate of 11,000 bits per second. That is still much slower than your computer's transfer rate, but it would be enough to send back more detailed images of the Mars surface. Mars Network researchers think that the transfer rate could eventually go to about 1 Megabyte (8,288,608 bits) per second and allow anyone to take a virtual trip to Mars.

An interplanetary Internet is like the Earth's Internet on a grand scale and with some improvements. Here are the three basic components of the proposed interplanetary Internet:

The DSN array of antennas would be used to send and receive data over the interplanetary Internet.

Photo courtesy NASA / DSN

The DSN is the international network of antennas used by NASA to track data and control navigation of interplanetary spacecraft. It is designed to allow for continuous radio communication with the spacecraft. However, recent space missions have lost communication with the DSN, including the Mars Climate Orbiter and the Mars Polar Lander missions in 1999. There are three global facilities, in California, Australia and Spain, that make up the DSN. Each facility is equipped with one 111-foot (34-meter) diameter high efficiency antenna, one 111-foot beam waveguide antenna (three in California), one 85-foot (26-meter) antenna, one 230-foot (70-meter) antenna and one 36-foot (11-meter) antenna.

In an interplanetary Internet, the DSN will be the Earth's gateway or portal to that Internet. In a paper published by the MITRE Corp., a company that is financing the Interplanetary Internet Study, researchers suggest that the DSN's antennas could be pointed at Mars to connect Earth and Mars for at least 12 hours each day. Satellites orbiting Mars should provide a full-time connection between the two planets. A Martian rover, probe or human colony will provide a Mars portal to the interplanetary Internet.

Under the Mars Network plan, the DSN will interact with a constellation of six microsatellites and one large Marsat satellite placed in low Mars orbit. These six microsats are relay satellites for spacecraft on or near the surface of the planet, and they will allow more data to come back from Mars missions. The Marsat will collect data from each of the smaller satellites and beam it to Earth. It will also keep Earth and distant spacecraft connected continuously and allow for high-bandwidth data and video of the planet, according to Mars Network officials. NASA could launch a microsat as early as 2003, with the six-microsat constellation orbiting Mars by 2009. In 2007, the Marsat is scheduled to be placed in a slightly higher orbit than the constellation. All of these dates are still very tentative.

Programmers are developing an Internet file transfer protocol to transmit the messages and overcome delays and interruptions. This protocol will act as the backbone of the entire system much as the Internet protocol (IP) and transmission control protocol (TCP) operate on Earth. IP and TCP, co-developed in the 1970s by Dr. Vinton Cerf, are the messenger service for our Earth-based Internet. These two protocols break up transmitted messages into packets of small data units and route them to a specified destination.

Cerf is part of the team of scientists who are developing a new protocol to enable reliable file transfer over the long distances between planets and spacecraft. This new space protocol must keep the Internet running even if some packets of data are lost during transmission. It must also block out noise picked up while crossing millions of miles. One idea for the space protocol is called the parcel transfer protocol (PTP), which will store and forward data at the gateway of each planet. The protocol would process an information request sent to a gateway and forward it to a final destination. The gateway would then check, process and forward information back down the path it came.